Method of and apparatus for phonograph suspension and low frequency improvement



3,300,222 NOGRAPH SUSPENSION 2 Sheets-Sheet 1 A 2 m F H. H. SCOTT AND APPARATUS FOR PHO AND LOW FREQUENCY IMPROVEMENT METHOD OF Jan. 24,

Filed June 18, 1964 INVENTOR HERMON H. SCOTT M fin-z,

ATTORNEYS FREQUENCY Jan. 24, 1967 H. H. SCOTT 3,300,222

METHOD OF AND APPARATUS FOR PHONOGRAPH SUSPENSION AND LOW FREQUENCY IMPROVEMENT Filed June 18, 1964 2 SheetsSheet 2 DE C IBELS OF SOUND OUTPUT l 1 I l 2 5 /0 20 L06 50- l00- 200- FREQUENCY INVENTOR HERMON H. scorr ATTORNEYS United States Patent Office Patented Jan. 24, 1967 3,300,222 METHOD OF AND APPARATUS FOR PHONO- GRAPH SUSPENSION AND LOW FREQUENCY IMPRGVEMENT Hermon H. Scott, Grasshopper Lane, Lincoln, Mass. 01773 Filed June 18, 1964, Ser. No. 376,166 12 Ciaims. (Cl. 274-39) The present invention relates to phonograph mounting structures adapted to provide improved low frequency response and, more particularly, to methods and apparatus for turntable mounting in cabinets and the like that are subjected to the vibration of loudspeaker assemblies and other types of vibration.

One of the serious problems that has plagued the phonograph console art has resided in the coupling of vibrations from loudspeaker assemblies to the sensitive tone arm of phonograph turntable structures as a result of the transmission of low frequency vibrations produced by the loudspeakers and coupled through the console structure to the tone arm. In effect, the vibrating loudspeaker, particularly at frequencies of the order of a few cycles per second, acts essentially as a vibrating mass that is coupled to the mass of the phonograph as a whole and tends to generate howl or mechanical feedback which can generate electrical feedback at the very low frequencies. Many suggestions have been offered throughout the years to try to minimize this effect, and these have included the design of the acoustic, mechanical or electrical portions of the phonograph reproducing apparatus to cut off at the low frequencies where the phonograph structure can be set into substantial mechanical vibration by the low-frequency sound emanating from the adjacent loudspeakers. Some attempts have been made to minimize the direct mechanical vibrations coupled through the cabinet from the loudspeaker assembly to the tone arm by springmounting the record player structure. In other cases, the loudspeaker assemblies have been shock mounted, generally also reducing the effective radiation of bass tones. These problems have become all the more acute over the past half a decade or so with the advent of stereophonic equipment, wherein two sets of loudspeakers are employed in the vicinity of the turntable, and the pickup is made sensitive to vibrations in a plane, rather than in a line as in the case of monophonic reproduction. The best that the art has been able to suggest over these years, accordingly, has been a compromise resulting in the sacrifice of a substantial band of the low frequencies below 100 cycles or so, or even, in some cases below 200 cycles or so, through the combination of electro-acoustic cutoff in the neighborhood of 100 cycles or so, or in some cases even higher, and the before-mentioned spring mounting of the record player upon the cabinet structure.

The present invention is directed to a novel method of and apparatus for vastly improving the low-frequency reproduction capability of phonograph assemblies associated in consoles or other cabinets and in particular with massive loudspeaker arrays, such as are employed in stereophonic reproduction; it being an object of the invention to provide greater low-frequency response in such systems than is currently available, and without deleterious feedback phenomena.

- .A further object of the inventionis to provide anovel apparatus of the character described in which the phonograph tone arm is inherently made far less sensitive to all types of external vibrations including the closing of phonograph covers or doors, floor vibrations and the like, which today plague reproduction, particularly with the new light-weight tone arms.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims; it being understood that the invention is equally applicable to other types of tone arm, stylus or acousticresponsive mechanisms and the like, all hereinafter generically termed, for purposes of completeness, phonographreproducing apparatus.

The invention will now be described in connection with the accompanying drawing, FIG. 1 of which is an isometric view, partly broken away, illustrating a constructional embodiment of the invention operating in accordance with the novel method here-involved;

FIGS. 2A and 2B are graphs comparing typical acoustic transmission and electro-acoustic response characteristics, respectively, of prior art systems and systems constructed in accordance with the present invention; and

FIG. 3 is a modified preferred construction.

Referring to FIG. 1, a conventional phonograph-reproducing apparatus is shown for illustrative purposes in the form of a turntable 1 containing a motor-driven record platform 3 and a sensitive tone arm 5, as is well known. It is this type of apparatus that, in accordance with the prior art, is normally mounted, as with the aid of depending springs 7, upon conventional present-day consoles or cabinets, with the electric circuitry or loudspeakers designed to cut off the response below the neighborhood of cycles per second or an even higher frequency, and with the shock-mounting providing about 12 decibels per octave change of mechanical vibration transmission at frequencies there-below, such that this transmission does not generate feedback in the console system. The overall averaged electro-acoustic frequency response of such construction is shown typically by the curve I in FIG. 2B, cutting off in the neighborhood of 100 cycles per second, more or less, with the corresponding acoustic transmission curve I of FIG. 2A showing a rising transmission characteristic with decreasing frequency therebelow. As before stated, in view of the transmission response I in such normal shock-mounted record players and the like, the very low frequencies, as below 100 cycles per second, are not reproduced in console systems. This has been considered to be an inherent restriction in the console art. 1

In accordance with the present invention, however, a further suspension has been added, as later explained, producing the resultant mechanical vibration transmission response shown in curve II, FIG. 2A. It will be noted that no rise in transmission occurs until frequencies well below 100 cycles per second,v in the neighborhood of 10 to 4 cycles per second, thus permitting :thelelectrical or electroacoustical circuits to be. provided with the response shown typically in curve II of FIG. 2B, reproducing frequencies well below 100 cycles per second down to the order of 20 or 30 cycles per second, without any deleterious acoustic feedback effects and thus with the advantage of providing very low-frequency response heretofore considered unattainable in such console or cabinet structures. 7 p 1 It remains; to e lain how the resultant transmission response of' curve 11 may be attained. Referring again to FIG. 1, it will be observed that the turntable or record player structure 1, unlike conventional systems, is not shock-mounted by the springs 7 upon the cabinet 2 itself. To the contrary, it is coupled by the springs 7 to a massive frame 9 that, in turn, is fitted within an aperture 6 in the cabinet 2 and is resiliently coupled to the cabinet 2 by means of further springs 11, shown disposed in positions, preferably peripherally, of the massive frame 9. The springs 11 are illustrated as preferably, but not necessarily, convergingly tapered toward their lower ends to prevent tilting of the same and to permit their securing by means of bolts 11' that are terminated by lock nuts 11" at the lower end, but that pass through apertures 9" in the flanges 9' of the massive frame 9 and lock to the upper surface of the cabinet 2 by means of heads 11" at the upper end. If desired, the springs may be filled with foam rubber or the like 11" to aid in damping. In this manner, the massive frame 9 is resiliently isolated from the cabinet 2, and the record changer 1 carrying the sensitive tone arm is isolated at 7 from the frame 9.

In accordance with the present invention, the frame 9 is provided with mass that is at least a substantial fraction of that of the record changer 1 and preferably comparable to it or greater, and the springs 11 are appropriately adjusted so that a low-pass mechanical filter mechanism is achieved with any peaks in the combination below the resonance peaking of the turntable structure 17 alone. Specifically, the mechanical resonant peak of the structure 17 alone is shown occurring in the neighborhood of 7 cycles per second at P and P in respective curves 1' and II of FIG. 2A; whereas the preferably comparable mass 9 and its spring suspension 11 in conjunction with turntable structure 17 is caused to produce peak mechanical resonance below 7 cycles per second region, preferably at substantially lower frequency, say 5 cycles per second, shown at the left-hand peak P in the curve II. A small, residual easily damped transmission peak occurring in the 15 cycle per second region may be caused by the mass of the frame 9 and the mass of the turntable structure 1 effectively operating in series at that frequency, but must be damped below a point where it would cause acoustic feed back. It has been found that the resultant effect of such a double suspension, with the mass-adding frame 9 and its resilient coupling 11 tuned comparable to or below the mechanical transmission frequency of the turntable 1 and its spring suspension 7, is to attain the desirable end of shifting the curve I of FIG. 2A to the left, obtaining a considerably steeper average attenuating slope of vibration transmission, as at II, and thus permitting the electrical response of the phonograph-reproducing system to be carried down to the order of or cycles per second, more or less, as demonstrated by curve II in FIG. 2 and without mechanical feedback causing deleterious effects, such as the howling before referred to. Thus, for the first time, extremely low bass reproduction is feasible in console structures, including those embodying double sets of speakers as in stereophonic systems, despite the fact that the speakers are in the same console with and very proximal to the sensitive tone arm 5 of the phonographreproducing apparatus.

As a typical illustration, the phonograph structure 1 may have a weight of the order of 15 pounds, more or less; whereas it has been found that if the frame 9 is made of or weighted with, say, cast iron or is of other suitably massive construction to attain the desired mass, and with a weight of the order of 12 pounds, the type of response shown in curve 11' may be attained.

In FIG. 3, the structure 1 is mounted upon even a wooden frame or platform 9 with weights 90 connected to and depending therefrom as part of the massive frame structure to provide the desired mass for the attainment of this phenomenon. This construction is less costly than the cast frame of FIG. 1.

Since the frame 9 is suspended from the cabinet 2, it is desirable at central regions of the frame 9 to provide further apertures 9" that may receive screw members 13 carrying washers 13 at their lower ends to enable clamping of the side flanges 9' against the under-side of portions of the cabinet 2 for transit purposes. In operation, the screw 13 is then released and the frame 9 becomes resiliently suspended from the cabinet 2 with the turntable 1,

in turn, resiliently suspended upon the frame 9, as before described.

Another feature of this invention is the inclusion of a rim 4 of sponge rubber, expanded plastic, or some similar resilient material, between the edge of the cabinet mounting aperture 6 and the casting 9 to prevent the casting striking the mounting board if the assembly is moved or pushed, and, when contacting both the edges of the aperture and the frame, to provide damping to reduce any undesirable resonance effects. This sponge rubber or simi lar stripping may be fastened either to the cabinet mounting 2, to the casting 9, or to both.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In phonograph-reproducing apparatus proximal to a source of low-frequency vibrations, the combination of turntable apparatus carrying a vibration-sensitive tone arm, a mass frame of weight at least comparable to that of the turntable apparatus, a supporting cabinet provided with an aperture for receiving the frame, means for resiliently mounting the frame to the cabinet and within the said aperture, and further means for resiliently mounting the turntable apparatus upon the frame in order to mini mize vibration coupling from the said cabinet to the tone arm.

2. In phonograph-reproducing apparatus proximal to a source of low-frequency vibrations, the combination of turntable apparatus carrying a vibration-sensitive tone arm, a mass frame of weight at least comparable to that of the turntable apparatus, a supporting cabinet provided with an aperture for receiving the frame, means for 're-' siliently mounting the frame to the cabinet and within the said aperture, and further means for resiliently mounting the turntable apparatus upon the frame in order to minimize vibration coupling from the said cabinet to the tone arm, the mass of the turntable apparatus and of the frame and its resilient mounting means being adjusted for a low frequency mechanical resonance below that of the turn= table apparatus and its resilient mounting means.

3. Apparatus as claimed in claim 2 and in which the said mechanical resonances are at frequencies in the ratio of at least about 1.3 to l.

4. Apparatus as claimed in claim 3 and in which the said frequencies are substantially 7 and 5 cycles per sec ond, respectively.

5. Apparatus as claimed in claim 2 and in which the reproducing apparatus has an electro-acoustic response extending down to about 30 cycles per second and the resultant mechanical resonance of the turntable appara= tus and the frame and their respective resilient mounting means lies below about 20 cycles per second.

6. Apparatus as claimed in claim 2 and in which the said cabinet comprises a compartment of a console containing a loudspeaker source of low-frequency vibrations.

7. Apparatus as claimed in claim 2 and in which the first-named resilient mounting means comprises springs, and the frame is provided with means for receiving bolts carrying springs disposed between the lower surfaces of the frame and the bottom of the bolts.

8. Apparatus as claimed in claim 7 and in which the said springs are convergingly compressingly tapered from top to bottom.

9. Apparatus as claimed in claim 7 and in which the said frame is provided with further apertures receiving bolts for locking the frame to the said supporting cabinet during transit and releasing the frame for resilient suspension during operation.

10. Apparatus as claimed in claim 7 and in which resilient damping means is inserted between the periphery of the said frame and the edges of the cabinet bounding the said aperture.

11. Apparatus as claimed in claim 2 and in which resilient damping means is inserted between the periphery of the said frame and the edges of the cabinet bounding the said aperture.

12. Apparatus 'as claimed in claim 2 and in which the mass frame comprises weight means connected to a platform.

References Cited by the Examiner UNITED STATES PATENTS 1,905,746 4/1933 Peets 274-39.1

5 FOREIGN PATENTS 814,972 6/1959 Great Britain.

902,766 8/1962 Great Britain.

10 JOHN M. HORAN, Primary Examiner.

CLIFFORD B. PRICE, Examiner. 

1. IN PHONOGRAPH-REPRODUCING APPARATUS PROXIMAL TO A SOURCE OF LOW-FREQUENCY VIBRATIONS, THE COMBINATION OF TURNTABLE APPARATUS CARRYING A VIBRATION-SENSITIVE TONE ARM, A MASS FRAME OF WEIGHT AT LEAST COMPARABLE TO THAT OF THE TURNTABLE APPARATUS, A SUPPORTING CABINET PROVIDED WITH AN APERTURE FOR RECEIVING THE FRAME, MEANS FOR RESILIENTLY MOUNTING THE FRAME TO THE CABINET AND WITHIN THE SAID APERTURE, AND FURTHER MEANS FOR RESILIENTLY MOUNTING THE TURNTABLE APPARATUS UPON THE FRAME IN ORDER TO MINIMIZE VIBRATION COUPLING FROM THE SAID CABINET TO THE TONE ARM. 